1 /* Convert a DNS packet to a human-readable representation.
2 Copyright (C) 2016-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
19 #include <support/format_nss.h>
21 #include <arpa/inet.h>
24 #include <support/check.h>
25 #include <support/support.h>
26 #include <support/xmemstream.h>
30 const unsigned char *data;
35 extract_16 (struct in_buffer *in, unsigned short *value)
39 *value = (in->data[0] << 8) | in->data[1];
46 extract_32 (struct in_buffer *in, unsigned *value)
50 unsigned a = in->data[0];
51 unsigned b = in->data[1];
52 unsigned c = in->data[2];
53 unsigned d = in->data[3];
54 *value = (a << 24) | (b << 16) | (c << 8) | d;
61 extract_bytes (struct in_buffer *in, size_t length, struct in_buffer *value)
63 if (in->size < length)
65 *value = (struct in_buffer) {in->data, length};
73 char name[MAXDNAME + 1];
77 extract_name (struct in_buffer full, struct in_buffer *in, struct dname *value)
79 const unsigned char *full_end = full.data + full.size;
80 /* Sanity checks; these indicate buffer misuse. */
82 (!(in->data < full.data || in->data > full_end
83 || in->size > (size_t) (full_end - in->data)));
84 int ret = dn_expand (full.data, full_end, in->data,
85 value->name, sizeof (value->name));
94 extract_name_data (struct in_buffer full, struct in_buffer *rdata,
95 const struct dname *owner, const char *typename, FILE *out)
98 if (extract_name (full, rdata, &name))
99 fprintf (out, "data: %s %s %s\n", owner->name, typename, name.name);
101 fprintf (out, "error: malformed CNAME/PTR record\n");
105 support_format_dns_packet (const unsigned char *buffer, size_t length)
107 struct in_buffer full = { buffer, length };
108 struct in_buffer in = full;
109 struct xmemstream mem;
110 xopen_memstream (&mem);
112 unsigned short txnid;
113 unsigned short flags;
114 unsigned short qdcount;
115 unsigned short ancount;
116 unsigned short nscount;
117 unsigned short adcount;
118 if (!(extract_16 (&in, &txnid)
119 && extract_16 (&in, &flags)
120 && extract_16 (&in, &qdcount)
121 && extract_16 (&in, &ancount)
122 && extract_16 (&in, &nscount)
123 && extract_16 (&in, &adcount)))
125 fprintf (mem.out, "error: could not parse DNS header\n");
130 fprintf (mem.out, "error: question count is %d, not 1\n", qdcount);
134 if (!extract_name (full, &in, &qname))
136 fprintf (mem.out, "error: malformed QNAME\n");
139 unsigned short qtype;
140 unsigned short qclass;
141 if (!(extract_16 (&in, &qtype)
142 && extract_16 (&in, &qclass)))
144 fprintf (mem.out, "error: malformed question\n");
147 if (qtype != T_A && qtype != T_AAAA && qtype != T_PTR)
149 fprintf (mem.out, "error: unsupported QTYPE %d\n", qtype);
153 fprintf (mem.out, "name: %s\n", qname.name);
155 for (int i = 0; i < ancount; ++i)
158 if (!extract_name (full, &in, &rname))
160 fprintf (mem.out, "error: malformed record name\n");
163 unsigned short rtype;
164 unsigned short rclass;
166 unsigned short rdlen;
167 struct in_buffer rdata;
168 if (!(extract_16 (&in, &rtype)
169 && extract_16 (&in, &rclass)
170 && extract_32 (&in, &ttl)
171 && extract_16 (&in, &rdlen)
172 && extract_bytes (&in, rdlen, &rdata)))
174 fprintf (mem.out, "error: malformed record header\n");
177 /* Skip non-matching record types. */
178 if ((rtype != qtype && rtype != T_CNAME) || rclass != qclass)
184 fprintf (mem.out, "address: %d.%d.%d.%d\n",
190 fprintf (mem.out, "error: A record of size %d: %s\n",
198 if (inet_ntop (AF_INET6, rdata.data, buf, sizeof (buf)) == NULL)
199 fprintf (mem.out, "error: AAAA record decoding failed: %m\n");
201 fprintf (mem.out, "address: %s\n", buf);
204 fprintf (mem.out, "error: AAAA record of size %d: %s\n",
209 extract_name_data (full, &rdata, &rname, "CNAME", mem.out);
212 extract_name_data (full, &rdata, &rname, "PTR", mem.out);
218 xfclose_memstream (&mem);